Economically important phycocolloids such as carrageenan and agar are produced by certain red algae. To extract a phycocolloid of interest, an alga is grown in a marine environment, is harvested and is processed. Different algal species may produce phycocolloids having different chemical properties and different physical characteristics, and/or may grow at an increased growth rate.
For example, carrageenan, a food industry colloid used as a clarifying agent, a suspending agent or a crystallization controlling agent, is a mixture of various length chains of sulfated disaccharide subunits. Different species of algae produce carrageenan chains having a different average number of sulphate groups per disaccharide subunit. The average sulfation per disaccharide typically varies from one (designated .kappa. carrageenan) to three (designated .lambda. carrageenan) sulfates per disaccharide. The intermediate value of two sulfates per disaccharide is designated .iota. carrageenan. The degree of sulfation determines the gel strength of the colloid extracted. A decrease in sulfation results in an increase in gel strength. Different gel strengths are desirable for different applications.
The ability to modify one species of algae by hybridizing the genetic material of a second species would permit the characteristics of the phycocolloid produced by the second species to be exhibited by the first species. Thus, for example, carrageenan having a higher than normal gel strength could be produced by an alga which typically produces a low or intermediate gel strength carrageenan. However, typically only closely related strains of a single species can sexually exchange genetic material successfully. Hence sexual hybridization has not produced commercially useful hybrid algae.
A number of techniques have been developed to create hybrid cells by fusing somatic cells. Referring to FIG. 1, Hwang et al. in Regeneration and Sexual Differentiation of Griffithsia japonica (Ceramiaceae, Rhodophyta) Through Somatic Cell Fusion, J. Phycol. 27, 441-447 (1991), describe a method for the somatic cell fusion of cells of the filamentous red alga Griffithsia japonica, by wound healing, so as to form a hybrid cell. In this technique 10, a cell 14 near the apical cell is wounded (step 16) and the cytoplasm removed. Within ten hours, adjacent cells 18 produce (step 22) repair cells 20 which grow into the lumen 21 of the wounded cell 14. The wounded cell is then transacted (step 24) and the separated filaments are immobilized in close contact on an agar plate (step 26). The repair cells 20 fuse (step 30), forming a hybrid cell 32 which can then be isolated (step 34) and cultured.
Similarly, referring to FIG. 1a, Susan D. Waaland in Parasexually Produced Hybrids between female and Male Plants of Griffithsia tenuis C. Agardh, a Red Alga, Planta 138, 65-68 (1978) describes the somatic cell fusion of male and female somatic cells of the filamentous red alga Griffithsia tenuis grown within a thin cylinder formed from the walls of the green alga Nitella. In this technique 36, two filaments 40, 40a are positioned (step 38) within the thin cylinder 42 and allowed to grow. The upper filament 40 produces (step 44) a rhizoid 46, while the lower filament produces a repair cell 48. The rhizoid 46 and the repair cell 48 grow toward one another. Eventually the rhizoid 46 and the repair cell 48 fuse (step 50) to form a hybrid cell 52, which can then be isolated and cultured. Thus both the Hwang and Waaland techniques of somatic cell fusion are limited to the fusion of cells of filamentous algae of a single genus.
Bradley and Cheney in Some Effects of Plant Growth Regulators on tissue cultures of the marine red alga Agardhiella subulata (Gigartihales, Rhodophyta), Hydrobiologica 204/205: 353-360, 1990, describe tissue culture by the growing of projections and calluses from a disk cut from red algae but do not describe any technique for creating somatic cell hybrids.
The present invention relates to somatic cell hybridization technique which are applicable to non-filamentous algae. The new techniques accomplish somatic cell hybridization of varieties of non-filamentous algae which have significant commercial value.